Liquid crystal display device and manufacturing method thereof

ABSTRACT

The present invention prevents the shaving of an alignment film caused by a columnar spacer in a liquid crystal display device of an IPS method using photo-alignment. A plinth higher than a pixel electrode is formed at a part where a columnar spacer formed over a counter substrate touches a TFT substrate. When an alignment film of a double-layered structure is applied over the pixel electrode and the plinth, the thickness of the alignment film over the plinth reduces by a leveling effect. When photo-alignment is applied in the state, a photodegraded upper alignment film over the plinth disappears and a lower alignment film having a high mechanical strength remains. As a result, it is possible to prevent the shaving of the alignment film.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2011-046857 filed on Mar. 3, 2011, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a liquid crystal display device and inparticular to a liquid crystal display device having a liquid crystaldisplay panel to which alignment control capability is given byirradiating an alignment film with light.

BACKGROUND OF THE INVENTION

In a liquid crystal display device, a TFT substrate over which pixelelectrodes and thin film transistors (TFTs), etc. are formed in a matrixshape and a counter substrate over which color filters, etc. are formedat locations corresponding to the pixel electrodes of the TFT substratein the manner of opposing the TFT substrate are disposed and a liquidcrystal is interposed between the TFT substrate and the countersubstrate. Then an image is formed by controlling the transmissivity oflight in liquid crystal molecules of each pixel.

A liquid crystal display device is widely used in various fields rangingfrom a large display device such as a TV to a cellular phone, a DSC(Digital Still Camera), etc. since it is flat and lightweight.Meanwhile, a liquid crystal display device has the problem of a viewangle characteristic. The view angle characteristic means thatbrightness varies or chromaticity varies when a screen is viewed fromthe front and then from an oblique direction. With regard to the viewangle characteristic, an In Plane Switching (IPS) method of operatingliquid crystal molecules by an electric field in the horizontaldirection has an excellent characteristic.

A conventional method of subjecting an alignment film used in a liquidcrystal display device to alignment treatment, namely giving alignmentcontrol capability, is a method of applying rubbing treatment. Thealignment treatment by rubbing is a method of applying alignmenttreatment by rubbing an alignment film with a cloth. In contrast, thereis a method called a photo-alignment method of giving alignment controlcapability to an alignment film in a noncontact manner. In the IPSmethod, the performance is better when a pre-tilt angle is small andhence the photo-alignment method is advantageously used.

Meanwhile, in a liquid crystal display device, it is important tocontrol the space between a TFT substrate and a counter electrode. Inmany cases, the space between a TFT substrate and a counter electrode iscontrolled by forming a columnar spacer on a counter substrate andforming a plinth to receive the columnar spacer on the TFT substrate. Aliquid crystal display device with a touch panel is frequently used inrecent years. When a liquid crystal display device is touched, the spacebetween the TET substrate and the counter substrate of the liquidcrystal display panel varies and the positional relationship between acolumnar spacer and a plinth deviates. As a result, touching fault suchas bleeding or uneven color appears in an image.

A liquid crystal display device having a configuration of setting thepositional relationship between a columnar spacer and a plinth so as tobe immovable by reducing the area of the plinth smaller than the area ofthe columnar spacer is described in JP-A No. 2007-164134.

When a columnar spacer is used, an alignment film for initially aligninga liquid crystal is formed also between the columnar spacer and a plinthformed on a TFT. When a liquid crystal display device is touched with afinger or the like, stress is imposed between the columnar spacer andthe plinth, giving rise to the phenomenon that the alignment film isshaved and shavings are caused. Such shavings cause the occurrence ofblight spots in a display region. Neither such a problem nor a measureis described in JP-A No. 2007-164134.

A photo-alignment film is formed in a double-layered structure in somecases. That is, the upper layer is formed with a material havingpolyamide acid ester containing cyclobutane and being likely to formphoto-alignment by ultraviolet rays as a precursor, and the lower layeris formed with a material having polyamide acid not containingcyclobutane and being mechanically strong as a precursor.

“CF 1” shows the structural formula of polyamide acid ester containingcyclobutane.

In “CF 1”, Ar represents a divalent aromatic group, R represents analkyl group having a carbon number of 1 to 8, and each of X1 to X4represents hydrogen or an alkyl group having a carbon number of 1 to 3independently.

“CF 2” shows the structural formula of polyamide acid not containingcyclobutane.

In “CF 2”, Y represents a divalent organic group and Z represents atetravalent organic group other than cyclobutane.

FIG. 16 is a schematic sectional view of a liquid crystal display devicehaving a double-layered alignment film. In FIG. 16, a passivation film107 is formed over a TFT substrate 100 including glass. Plural layersincluding a common electrode are formed between the passivation film 107and the TFT substrate 100 but are omitted in FIG. 16. Pixel electrodes108 are formed over the passivation film 107. An alignment film 113including two layers of a lower alignment film 111 and an upperalignment film 112 is formed in the manner of covering the pixelelectrodes 108. The upper alignment film 112 includes a photoreactivematerial produced by using polyamide acid ester as a precursor, has afilm thickness reduced by photoreaction, and has a low mechanicalstrength. On the other hand, the lower alignment film 111 includes anon-photoreactive material produced by using polyamide acid as aprecursor and the film thickness thereof does not reduce even after theirradiation of ultraviolet rays.

In FIG. 16, a black matrix 201 and a color filter 202 are formed over acounter substrate 200. An overcoat film 203 is formed over the blackmatrix 201 and the color filter 202 but is omitted in FIG. 16. A partwhere the color filter 202 is formed is a transparent region 400 and animage is formed by light transmitting the transparent region 400. A partwhere the black matrix 201 is formed is a nontransparent region 500.

In FIG. 16, a columnar spacer 204 to define a space between the TFTsubstrate 100 and the counter substrate 200 is formed over the blackmatrix 201. The tip of the columnar spacer 204 touches the upperalignment film 112 over the TFT substrate 100 and a plinth 114 made ofthe same material as the pixel electrodes 108 is formed at the part. Theheight of the top end of the plinth is the same as the height of the topends of the pixel electrodes.

In the upper alignment film 112, photodecomposition reaction isgenerated by the irradiation of ultraviolet rays, the molecular weightdecreases, and the alignment film strength lowers. If a heat shock testof −40° C. to 85° C. for example is applied to such a liquid crystaldisplay device, the upper alignment film 112 peels off at the part ofthe plinth 114 and a very fine blight spot caused by the shavings isformed. The shavings of the alignment film are formed in the region Rsurrounded by the dotted line in FIG. 16. That is, it is estimated thata panel warps repeatedly because of the in-plane temperaturedistribution of the panel caused by a heat shock test, that the columnarspacer 204 formed on the side of the counter substrate 200 shaves thealignment film 113 over the plinth 114 on the side of the TFT substrate100, that a fraction of the alignment film 113 floats in a liquidcrystal, and that hence a blight spot occurs.

SUMMARY OF THE INVENTION

In view of the above situation, a problem of the present invention is toprevent a blight spot caused by the shaving of an alignment film fromoccurring in a liquid crystal display device using photo-alignment.

The present invention overcomes the above challenge and therepresentative means is as follows. That is, the means is a liquidcrystal display device including pixels formed in regions surrounded byscanning lines and picture signal lines; a pixel electrode formed ateach of the pixels over an insulation film; a TFT substrate supplying apicture signal to each of the pixel electrode through a TFT; a countersubstrate formed opposite the TFT substrate; and a liquid crystal layerinterposed between the TFT substrate and the counter substrate, wherein:a columnar spacer to retain a space from the TFT substrate is formedover the counter substrate; a plinth facing a tip of the columnar spaceris formed over the TFT substrate and an alignment film is formed so asto cover the plinth, the pixel electrodes, and the insulation film;photo-alignment treatment is applied to the alignment film; a top end ofthe plinth is higher than top ends of the pixel electrodes; thealignment film includes a lower alignment film formed by using polyamideacid as a precursor and an upper alignment film formed by usingpolyamide acid ester as a precursor; and, when the thickness of thelower alignment film is defined as p1 and the thickness of the upperalignment film is defined as p2, p2/p1 over the plinth is smaller thanp2/p1 over the insulation film.

The present invention, in a liquid crystal display device having acolumnar spacer and using a photo-alignment film, makes it possible to:prevent the shaving of the alignment film caused by the columnar spacer;and hence improve the manufacturing yield of the liquid crystal displaydevice. Further, it is possible to: prevent the shaving of the alignmentfilm caused by the columnar spacer because of a temperature cycle aftershipping; and hence prevent market failure from occurring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a TFT substrate showing the state ofapplying an alignment film according to the present invention;

FIG. 2 is a sectional view of a TFT substrate showing the state afterphoto-alignment treatment is applied to the state shown in FIG. 1;

FIG. 3 is a sectional view of a liquid crystal display device showingthe state of disposing a counter substrate to the state shown in FIG. 2;

FIG. 4 is a plan view of a pixel part according to Example 1;

FIG. 5 is a sectional view taken on line A-A in FIG. 4;

FIG. 6 is a plan view of a pixel part according to Example 2;

FIG. 7 is a sectional view taken on line B-B in FIG. 6;

FIG. 8 is a plan view of a pixel part according to Example 3;

FIG. 9 is a sectional view taken on line C-C in FIG. 8;

FIG. 10 is a plan view of a pixel part according to Example 4;

FIG. 11 is a sectional view taken on line D-D in FIG. 10;

FIG. 12 is a sectional view taken on line E-E in FIG. 10;

FIGS. 13A and 13B are an example of the shape of a plinth;

FIGS. 14A and 14B are another example of the shape of a plinth;

FIGS. 15A and 15B are yet another example of the shape of a plinth; and

FIG. 16 is a sectional view of a liquid crystal display device not usingthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 3 are sectional views on the side of a TFT substrate 100showing the process for forming a substantial part in the presentinvention. In FIG. 1, a passivation film 107 is formed over the TFTsubstrate 100 made of glass. A layer formed between the passivation film107 and the TFT substrate 100 is omitted in FIG. 1. In FIG. 1, pixelelectrodes 108 are formed over the passivation film 107. The part wherethe pixel electrodes 108 are formed is a pixel region.

A plinth 114 for a columnar spacer 204 is formed at a part where thepixel electrodes 108 are not formed. The part of the plinth 114 includesa film formed with the same material as the pixel electrodes 108 andanother film. Consequently, the tip of the plinth 114 is higher than thetips of the pixel electrodes 108. An alignment film 113 is formed in themanner of covering the pixel electrodes 108 and the plinth 114.

The alignment film 113 includes a lower alignment film 111 formed byusing polyamide acid not having photoreactivity but being mechanicallystrong as a precursor and an upper alignment film 112 formed by usingpolyamide acid ester having photoreactivity as a precursor. The materialfor the alignment film is a substance produced by blending polyamideacid ester and polyamide acid at the ratio of 4 to 6 and, when thesubstance is applied over the pixel electrodes 108 and others, thesubstance is separated into two upper and lower layers so that the upperlayer may be polyamide acid ester and the lower layer may be polyamideacid. Since the quantity of polyamide acid ester is smaller than thequantity of polyamide acid, the thickness of the upper alignment 112 issomewhat smaller than the thickness of the lower alignment film 111.Further, since the part of the plinth 114 is higher than the part of thepixel electrodes 108, the thickness of the alignment film 113 at thepart of the plinth 114 is small by a leveling effect. Successively theformed alignment film 113 is baked at about 200° C. to 230° C. FIG. 1shows the state.

FIG. 2 is a sectional view showing the state of applying alignmenttreatment by irradiating the alignment film 113 in the state of FIG. 1with ultraviolet rays and thus irradiating the upper alignment film 112formed by using polyamide acid ester as the precursor with theultraviolet rays. When the upper alignment film 112 is irradiated withultraviolet rays, the upper alignment film 112 causes photodecompositionreaction, the molecular weight reduces, and the film strength lowers.Further, a part of the upper alignment film 112 causing thephotodecomposition reaction evaporates. Consequently, the thickness ofthe upper alignment film 112 reduces to a certain extent.

Since the alignment film 113 at the part of the plinth 114 is thin fromthe beginning, the upper alignment film 112 is also thinner than theother part. Consequently, when the upper alignment film 112 decomposesand evaporates by photoreaction, the upper alignment film 112 almostdisappears at the part of the plinth 114 as shown in FIG. 2. On theother hand, the lower alignment film 111 formed by using polyamide acidas the precursor does not photoreact and hence the lower alignment film111 retains the original thickness and strength. Consequently, thecomponent of the lower alignment film 111 having a high mechanicalstrength is predominantly large in quantity over the plinth 114.

Meanwhile, the alignment film 113 retains the double-layered structureat parts other than the plinth 114 including the pixel part. That is, atthe part of the pixels too, the upper alignment film 112 photoreacts,photoreaction treatment is applied, a part of the upper alignment film112 evaporates, and the thickness reduces to a certain extent. At thepixel region, however, since the thickness of the upper alignment film112 is larger than the part of the plinth 114 from the beginning, evenwhen a part evaporates, a certain film thickness necessary for aligningliquid crystal molecules is retained in the upper alignment film.

FIG. 3 is a sectional view showing the state of combining a countersubstrate 200 over which a columnar spacer 204 is formed with a TFTsubstrate 100 thus formed. In FIG. 3, a liquid crystal layer 300 isinterposed between the TFT substrate 100 and the counter substrate 200.The configuration on the side of the TFT substrate 100 in FIG. 3 is thesame as that explained in FIG. 2. A black matrix 201 to form anontransparent region 500 and a color filter 202 to form a transparentregion 400 are formed over the counter substrate 200. An overcoat film203 is omitted in FIG. 3. Further, an alignment film 113 is formed alsoover the counter substrate 200 but is omitted in FIG. 3. The columnarspacer 204 is formed at the part where the black matrix 201 is formed inFIG. 3.

The tip of the columnar spacer 204 touches the part of the plinth 114over the TFT substrate 100 and the alignment film 113 at the part mostlyincludes the lower alignment film 111 formed by using polyamide acidhaving a high mechanical strength as the precursor as it has beenexplained in FIG. 2. That is, the upper alignment film 112 formed byusing polyamide acid ester having a low mechanical strength as theprecursor scarcely exists and hence it is possible to minimize theprobability of generating the shaving of the alignment film 113 causedby the columnar spacer 204. Meanwhile, the black matrix 201 is formedover the counter substrate 200 corresponding to the part of the plinth114 and hence light leakage does not occur even when liquid crystalmolecules do not receive initial alignment.

In this way, the present invention makes it possible to prevent theshaving of an alignment film 113 occurring because a columnar spacer 204touches the photo-alignment film 113. Further, it is possible to preventblight spots from forming by the shavings. Concrete structures of thepresent invention are hereunder explained in reference to examples of aliquid crystal display device of an IPS method.

EXAMPLE 1

FIG. 4 is a plan view of a pixel part according to Example 1 and FIG. 5is a sectional view of a liquid crystal display device corresponding tothe cross-section taken on line A-A in FIG. 4. In FIG. 4, a pixel isformed in a region surrounded by scanning lines 10 and picture signallines 20. In a pixel, a common electrode 101 made of Indium Tin Oxide(ITO) is formed in the shape of a solid plane on the lower side and acommon line 102 to supply common potential to the common electrode 101is formed in an overlapping manner at an end of the common electrode101. A pixel electrode 108 having slits is formed over the commonelectrode 101 while an insulation film is interposed. When a picturesignal is supplied to the pixel electrode 108, a line of electric forceis generated at a liquid crystal layer 300 between the pixel electrode108 and the common electrode 101 through the slits, thereby liquidcrystal molecules rotate, the quantity of light from a backlight iscontrolled, and thereby an image is formed.

In FIG. 4, a TFT is formed over a scanning line 10. A semiconductorlayer 104 is formed over the scanning line 10 while a gate insulationfilm is interposed in between. A drain electrode 105 is formed bybranching a picture signal line 20. A source electrode 106 is formedopposite the drain electrode 105 and the source electrode 106 extends ina pixel region and is electrically continuous with the pixel electrode108 through a through hole 109.

In FIG. 4, a plinth 114 made of the same material as the pixel electrode108 is formed over the scanning line 10. The plinth 114 is hereunderreferred to as a pixel electrode plinth 1141. An insulation film existsbetween the pixel electrode plinth 1141 and the scanning line 10.Further, an alignment film 113 is formed over the pixel electrode plinth1141. The tip of a columnar spacer 204 formed over a counter substrate200 touches the part corresponding to the pixel electrode plinth 1141.

FIG. 5 is a sectional view of a liquid crystal display devicecorresponding to the cross-section taken on line A-A in FIG. 4. In FIG.5, a lower polarizing plate 120 is formed outside a TFT substrate 100and an upper polarizing plate 220 is formed outside a counter substrate200. A liquid crystal layer 300 is interposed between the TFT substrate100 and the counter substrate 200. In FIG. 5, a common electrode 101made of ITO that is a transparent electrode is formed over the TFTsubstrate 100. A common line 102 to supply common potential to thecommon electrode 101 overlaps with an end of the common electrode 101.The common electrode 101 is formed in the manner of being electricallyinsulated from the scanning line 10.

The scanning line 10 has a double-layered structure; the lower layerincludes an electrically-conductive layer 1011 made of ITO similarly tothe common electrode 101 and the upper layer is made of the same metalas the common line 102. A metal constituting the scanning line 10 isMoW, Al alloy, etc., for example.

A gate insulation film 103 is formed in the manner of covering thescanning line 10 and the common electrode 101 and a passivation film 107is formed over the gate insulation film 103. The pixel electrode 108made of ITO that is a transparent electrode is formed over thepassivation film 107. Meanwhile, a pixel electrode plinth 1141 is formedwith ITO similarly to the pixel electrode 108 also over the passivationfilm 107 over the scanning line 10. As it is obvious from FIG. 5, thetop end of the pixel electrode plinth 1141 is higher than the top end ofthe pixel electrode 108.

Since the alignment film 113 is applied in such a state, as shown inFIG. 1, the thickness of the alignment film 113 over the pixel electrodeplinth 1141 reduces and, when the alignment film 113 is irradiated withultraviolet rays in order to apply photo-alignment, the upper alignmentfilm 112 formed by using polyamide acid ester as the precursor almostdisappears over the pixel electrode plinth 1141. Consequently, over thepixel electrode plinth 1141, the lower alignment film 111 formed byusing polyamide acid having a high mechanical strength as the precursormostly exists and shavings are not easily caused even when the columnarspacer 204 touches the alignment film 113. Consequently, blight spotscaused by the shavings of the alignment film 113 do not occur. Incontrast, at the part of the pixel electrode 108 of a low height, thealignment film 113 is thick and hence the double-layered structure ofthe alignment film 113 is retained even after photo-alignment is appliedby the irradiation of ultraviolet rays. That is, the upper alignmentfilm 112 being subjected to photo-alignment treatment and having aprescribed thickness exists and hence liquid crystal molecules can bealigned.

In FIG. 5, a black matrix 201 and a color filter 202 are formed over thecounter substrate 200. The black matrix 201 covers the part of the pixelelectrode plinth 1141 and hence light from backlight does not permeateeven when liquid crystal is not aligned at the part. In FIG. 5, anovercoat film 203 is formed in the manner of covering the color filter202 and a columnar spacer 204 is formed over the overcoat film 203.

An alignment film 113 is formed in the manner of covering the overcoatfilm 203 and the columnar spacer 204. The alignment film 113 on the sideof the counter substrate 200 also has a double-layered structure but, inFIG. 5, the alignment film 113 is drawn as a single-layered structure inorder to avoid complicating the drawing. At the counter substrate 200,when the alignment film 113 is applied, the alignment film 113 having aprescribed thickness is formed over the overcoat film 203, but thecolumnar spacer 204 is high, and hence the alignment film 113 scarcelyexists at the tip of the columnar spacer 204 due to a leveling effect.Further, even if the alignment film 113 remains at the tip of thecolumnar spacer 204, by the irradiation of ultraviolet rays for applyingphoto-alignment, the upper alignment film 112 formed by using polyamideacid ester as the precursor disappears and the lower alignment film 111formed by using polyamide acid having a high mechanical strength as theprecursor remains mostly. Consequently, it never happens that thealignment film 113 remaining on the side of the columnar spacer 204 isshaved and blight spots are caused by the shavings.

In this way, over both the TFT substrate 100 and the counter substrate200, the structure is configured so that, at the part where the columnarspacer 204 touches the side of the TFT substrate 100, the upperalignment film 112 formed by using polyamide acid ester as the precursormay scarcely exist and blight spots caused by the shavings of thealignment film 113 may hardly occur.

EXAMPLE 2

FIG. 6 is a plan view of a pixel part according to Example 2. Theconfiguration in FIG. 6 is the same as that in FIG. 4 except the part ofa plinth 114. In FIG. 6, the plinth 114 forms a composite plinthincluding a pixel electrode plinth 1141 and a plinth made of asemiconductor, namely a semiconductor plinth 1142. The tip of the plinth114 is higher than that in Example 1 to the extent and a leveling effectwhen an alignment film 113 is applied is more likely to appear.

FIG. 7 is a sectional view of a liquid crystal display devicecorresponding to the cross-section taken on line B-B in FIG. 6. Thefigure is the same as FIG. 5 except the plinth part formed over ascanning line 10. In FIG. 7, a semiconductor is formed over a gateinsulation film 103 over the scanning line 10 and it constitutes asemiconductor plinth 1142. A passivation film 107 is formed over thesemiconductor plinth 1142 and a pixel electrode plinth 1141 is formedover the passivation film 107 in the same manner as Example 1. That is,in the present example, the plinth 114 includes both the semiconductorplinth 1142 and the pixel electrode plinth 1141 and the height of theplinth 114 is higher than that in Example 1. By so doing, it is possibleto exhibit the leveling effect more effectively when an alignment film113 is applied. Consequently, at the part which the tip of a columnarspacer 204 touches, the probability that an upper alignment film 112exists further lowers and the probability of the exfoliation of thealignment film 113 also lowers.

EXAMPLE 3

FIG. 8 is a plan view of a pixel part according to Example 3. Theconfiguration in FIG. 8 is the same as that in FIG. 6 except the part ofa plinth 114. In FIG. 8, the plinth 114 forms a composite plinthincluding a pixel electrode plinth 1141 and a plinth made of a materialidentical to a picture signal line 20, namely a picture signal lineplinth 1143. The tip of the plinth 114 is higher than that in Example 1to the extent and the leveling effect when an alignment film 113 isapplied is more likely to appear.

FIG. 9 is a sectional view of a liquid crystal display devicecorresponding to the cross-section taken on line C-C in FIG. 8. Thefigure is the same as FIG. 7 in Example 2 except the plinth part formedover a scanning line 10. Both the cases of FIGS. 9 and 7 are thecomposite plinths but the difference in FIG. 9 from in FIG. 7 is thatthe lower side of the composite plinth is not a semiconductor plinth1142 but a picture signal line plinth 1143 in FIG. 9.

In Example 3, the tip of the plinth 114 is higher than that in Example 1to the extent corresponding to the existence of the picture signal lineplinth 1143 and accordingly it is possible to yield the effect ofleveling more effectively when an alignment film 113 is applied.Consequently, at the part which the tip of a columnar spacer 204touches, the probability that an upper alignment film 112 exists furtherlowers and the probability of the exfoliation of the alignment film 113also lowers.

EXAMPLE 4

FIG. 10 is a plan view of a pixel part according to Example 4. Theconfiguration in FIG. 10 is the same as that in FIG. 4 of Example 1except the part of a plinth 114. In the present example, the plinth 114is formed over a picture signal line 20. The purpose is to increase theheight of the plinth 114 and to enhance the effect of leveling when analignment film 113 is applied. At a counter substrate 200, the positionof a columnar spacer 204 is also different from Example 1 and the likein conformity with the position of the plinth 114.

FIG. 11 is a sectional view taken on line D-D in FIG. 10 and FIG. 12 isa sectional view taken on line E-E in FIG. 10. FIG. 11 is a sectionalview of a part where a plinth 114 is formed and FIG. 12 is a sectionalview of a part where a pixel electrode 108 is formed. In FIG. 11 showingthe cross-section of the part where the plinth 114 is formed, six layersof an electrically-conductive layer 1011, a scanning line 10, a gateinsulation film 103, a picture signal line 20, a passivation film 107,and a pixel electrode plinth 1141 are formed from the surface of a TFTsubstrate 100 to the upper face of the pixel electrode plinth 1141. Incontrast, in FIG. 12 showing the cross-section of the pixel part, onlyfour layers of a common electrode 101, a gate insulation film 103, apassivation film 107, and a pixel electrode 108 are formed from thesurface of the TFT substrate 100.

Consequently, the distance t2 between the surface of the TFT substrate100 and the upper part of the plinth 114 in FIG. 11 is larger than thedistance t1 between the surface of the TFT substrate 100 and the upperpart of the pixel electrode 108 in FIG. 12 to the extent correspondingto the sum of the thickness of the scanning line 10 and the thickness ofthe picture signal line 20. By so doing, it is possible to sufficientlyexhibit a leveling effect when an alignment film 113 is applied. As aresult, after photo-alignment is applied by the irradiation ofultraviolet rays, as shown in FIG. 11, at the part of the plinth 114which the columnar spacer 204 touches, an upper alignment film 112scarcely exists and only a lower alignment film 111 having a highmechanical strength exists. In contrast, since the part of the pixelelectrode 108 is lower than the part of the plinth 114, thedouble-layered structure of the alignment film 113 is retained and it ispossible to cause initial alignment of liquid crystal molecules by theupper alignment film 112.

In this way, in the present example too, while an initial alignmenteffect to liquid crystal molecules is retained, it is possible toprevent: the shaving of an alignment film 113 caused by a columnarspacer 204; and the occurrence of bright spots.

EXAMPLE 5

Although the present invention has been explained in the context of thestructure of the pixel part of a liquid crystal display device inExamples 1 to 4, in the present example, the shape of the part of aplinth 114 and the component of an alignment film 113 are explained indetail. FIG. 13 is the case where the planar shape of a plinth 114 issquare. FIG. 13A is a plan view and FIG. 13B is a sectional view takenon line F-F in FIG. 13A. In FIG. 13, the sectional shape of the plinth114 is trapezoidal. That is, the radius of the plinth upper face 116 issmaller than the radius of the plinth lower face 115. In such a case,the radius of the narrowest part of the plinth 114 is defined as w thatis the radius of the upper face. Further, in FIG. 13B, the height h ofthe plinth 114 is defined as the difference in height between the upperface of a pixel electrode 108 in a pixel region and the upper face ofthe plinth 114 in reference to FIG. 1 for example.

FIG. 14 is the case where the plane of a plinth 114 is rectangular. FIG.14A is a plan view of the plinth 114 and FIG. 14B is a sectional viewtaken on line G-G in FIG. 14A. In FIG. 14, the narrowest part of theplinth 114 is the short radius w of the plinth upper face 116. Further,the definition of the height h of the plinth 114 in FIG. 14B isidentical to that in FIG. 13.

FIG. 15 is the case where a plinth 114 is round. FIG. 15A is a plan viewof the plinth 114 and FIG. 15B is a sectional view taken on line H-H inFIG. 15A. In FIG. 15, the narrowest part of the plinth 114 is thediameter w of the upper face of the plinth 114. Further, the definitionof the height h of the plinth 114 in FIG. 15B is identical to that inFIG. 13.

Although the cross-sectional shape of a plinth 114 is trapezoidal in theabove examples of the plinth 114, it may also be rectangular. Further, aplinth 114 in the above cases is just for showing an example of aheight, a narrowest part, and the like and it does not mean that theshape of a plinth 114 is limited to the above three cases.

The present invention is characterized by: over a plinth 114, minimizingthe existence of an upper alignment film 112 to the smallest possibleextent and bringing a lower alignment film 111 having a high mechanicalstrength into contact with a columnar spacer 204; and over a pixelelectrode 108, retaining the thickness of the upper alignment film 112so as to be enough for aligning liquid crystal molecules and retaining adouble-layered structure. In order to realize such a configuration, theshape of a plinth 114, the coating thickness of an alignment film 113,and a blend ratio of polyamide acid ester to polyamide acid in thematerial for the alignment film 113 are important.

Here, the following parameters are introduced:

a: As a plinth aspect ratio, plinth height h/plinth narrowest part widthw;

b: Alignment film thickness over plinth/alignment film thickness overinsulation film in pixel region. Here, an insulation film in a pixelregion is a passivation film 107 in Examples 1 to 4 and other cases butanother insulation film may exist instead of the passivation film 107occasionally;

c: Ratio of polyamide acid ester in alignment film material. Here, thealignment film material is a mixture of polyamide acid ester andpolyamide acid and c is the ratio of polyamide acid ester in themixture. That is, when the quantity of polyamide acid ester is definedas x and the quantity of polyamide acid is defined as y, the expressionc=x/(x+y) is obtained. c satisfies the expression 0.2<c<0.8, preferablythe expression 0.3<c<0.7; and

d: Alignment film thickness d over insulation film in pixel region. dsatisfies the expression 30 nm<d<150 nm, preferably the expression 40nm<d<130 nm. Here, the expression cd>10 nm has to be satisfied. drepresents the film thickness after photo-alignment, namely the filmthickness in a liquid crystal display device. That is, the purpose is toleave at least 10 nm of the upper alignment film 112 formed by usingpolyamide acid ester as the precursor and sufficiently retain theinitial alignment capability of liquid crystal in the pixel region.

When a, b, c, and d are defined as stated above, the relationshipbetween the ratio c of polyamide acid ester in an alignment filmmaterial and other parameters is represented by the expressionc<80/(b(d+40)), preferably c<60/(b(d+40)). Here, when the narrowest partw of a plinth 114 is not more than 10 μm, b=0.9 and, when the narrowestpart w of a plinth 114 is more than 10 μm, b=1/(13.9(a+0.08))+0.1 andb<0.9.

As stated above, by selecting a plinth shape, an alignment filmmaterial, and an alignment film thickness, it is possible to obtain aconfiguration of such a liquid crystal display device as shown inExamples 1 to 4. The concrete features of a liquid crystal displaydevice manufactured by the production method shown above are as follows.

A: The ratio of the thickness of an upper alignment film 112 to thethickness of a lower alignment film 111 is different between over aplinth 114 and over an insulation film in a pixel region. That is, theratio of an upper alignment film 112 over a plinth 114 is smaller thanthat over an insulation film in a pixel region.

B: The ratio of an upper alignment film 112 formed by using polyamideacid ester as a precursor in an alignment film 113 over a plinth 114 is0.3 or less, preferably 0.2 or less, and more preferably 0.1 or less.

C: The thickness of an upper alignment film 112 formed by usingpolyamide acid ester as a precursor in an alignment film 113 over aplinth 114 is 30 nm or less, preferably 20 nm or less, and morepreferably 10 nm or less.

By the above configuration, in a liquid crystal display device using aphoto-alignment film 113, it is possible to inhibit the exfoliation ofthe alignment film caused by a columnar spacer 204 and prevent theoccurrence of blight spots caused by the shavings of the alignment film.Here, the plinths 114 described in Examples 1 to 4 are only examples andit is also possible to use the plinths 114 described in Examples 1 to 4compositely. That is, with regard to a plinth 114, it is possible toincrease the height of the plinth 114, enhance the leveling effect of analignment film 113, and increase the effect of the present invention bystacking and using a pixel electrode plinth 1141, a semiconductor plinth1142, a picture signal line plinth 1143, and the like. Further, over apicture signal line 20, it is possible to use a pixel electrode plinth1141 and a semiconductor plinth 1142 compositely.

What is claimed is:
 1. A liquid crystal display device comprising:pixels formed in regions surrounded by scanning lines extending in afirst direction and arrayed in a second direction and picture signallines extending in the second direction and arrayed in the firstdirection; a pixel electrode formed at each of the pixels over aninsulation film and a passivation film; a TFT substrate supplying apicture signal to each of the pixel electrodes through a TFT; a countersubstrate formed opposite the TFT substrate; and a liquid crystal layerinterposed between the TFT substrate and the counter substrate, whereina columnar spacer to retain a space from the TFT substrate is formedover the counter substrate; a plinth facing a tip of the columnar spaceris formed over the TFT substrate and an alignment film is formed so asto cover the plinth, the pixel electrodes, the insulation film, and thepassivation film; photo-alignment treatment is applied to the alignmentfilm; a top end of the plinth is higher than top ends of the pixelelectrodes; the alignment film includes a lower alignment film formed byusing polyamide acid as a precursor and an upper alignment film formedby using polyamide acid ester as a precursor; when the thickness of thelower alignment film is defined as p1 and the thickness of the upperalignment film is defined as p2, p2/p1 over the plinth is smaller thanp2/p1 over the insulation film; and wherein p2/(p1+p2) is 0.3 or lessover the plinth.
 2. The liquid crystal display device according to claim1, wherein p2/(p1+p2) is 0.2 or less over the plinth.
 3. The liquidcrystal display device according to claim 1, wherein p2/(p1+p2) is 0.1or less over the plinth.
 4. The liquid crystal display device accordingto claim 1, wherein p2 is 30 nm or less over the plinth.
 5. The liquidcrystal display device according to claim 1, wherein p2 is 20 nm or lessover the plinth.
 6. The liquid crystal display device according to claim1, wherein p2 is 10 nm or less over the plinth.
 7. The liquid crystaldisplay device according to claim 1, wherein the plinth: is formed overthe scanning lines; and, as a constituent component, includes a materialidentical to the pixel electrodes, a material identical to thesemiconductor layer of the TFT, or a material identical to the picturesignal lines.
 8. The liquid crystal display device according to claim 1,wherein the plinth: is formed over the picture signal lines; and, as aconstituent component, includes a material identical to the pixelelectrodes or a material identical to the semiconductor layer of theTFT.